1. Field of the Invention
The present invention relates to a resin composition for a refrigerant-transporting hose useful as a material for a refrigerant-transporting hose for a vehicle such as an automobile and a method of producing the resin composition, and a refrigerant-transporting hose formed of the resin composition.
2. Description of the Related Art
In recent years, in association with a tightened regulation on the release of ozone layer-depleting gases, a demand on the barrier property (refrigerant permeation resistance) of a refrigerant-transporting hose (air-conditioner hose) for an automobile or the like has become stringent. Accordingly, a resin having high crystallinity such as a polyamide has been used for a resin material for forming a resin layer of the refrigerant-transporting hose.
However, it has been known that a refrigerant for an automobile deteriorates owing to long-term use, which generates an acid. As an amide bond is apt to be decomposed by the acid, a situation in which the polyamide resin layer of the refrigerant-transporting hose is apt to be deteriorated is established. Bending the refrigerant-transporting hose whose polyamide resin layer has deteriorated results in cracking the hose. Moreover, the refrigerant-transporting hose for a vehicle such as an automobile is typically used in a high-temperature environment, and hence the decomposition of the amide bond by the acid is apt to be promoted.
Accordingly, in recent years, a semi-aromatic polyamide resin such as a polyamide 9T (PA9T), which is excellent in refrigerant permeation resistance and acid resistance, has been attracting attention as a material for the refrigerant-transporting hose (see, for example, Japanese Laid-open Patent Application No. 2006-212966 and Japanese Laid-open Patent Application No. 2007-90563).
However, when the semi-aromatic polyamide resin such as the PA9T is extruded upon production of the hose, the resin crystallizes (changes from a molten state to a solid state) immediately after the extrusion because the resin has a high melting point and a high crystallization rate. The resin layer thus extruded often has a weld line that can be visually observed. Accordingly, deformation (thickness deviation) at the time of its molding and local reductions in physical properties of the hose are apt to occur.
In addition, when the semi-aromatic polyamide resin such as PA9T is used as a hose material, for example, the following problems arise in addition to the problem concerning extrusion processability at the time of production of the hose as described above. The semi-aromatic polyamide resin has high rigidity and thus poor flexibility, and it is vulnerable to an impact at low temperature. The semi-aromatic polyamide resin is not suited for any application of the refrigerant-transporting hose owing to the problems, and hence its improvement has been demanded.